Right now I have a 55 gallon tank that I got two Tangs in. A yellow eye and a yellow tang.
I saved the both from a smaller tank and the Yellow was beat up from other fish. I would say their life is 100% times better. I am upgrading to a 75 gallon soon (I was going to go 150, but life happens). So with a 75 gallon they will have more space! I am still going to upgrade to a 150 gallon, I just got to wait a little longer.
So what I am trying to say, I think you will be fine with two Tangs in a 75 gallon. As long as you put them in together at the same time! I wouldn't do a Yellow Tang in a 75, I am only doing it because both tangs were in real bad shape and I felt really bad for them. So I bought them and thankfully they are thriving!
If I were you, I would at least get the Yellow Eye Very cool looking Tang!
Also here is a list of Tangs that Live Aquaria says is good.